Advice wanted on deck joist hangers

[Prybar]

Hi. I'm looking to install a deck of 4570 between two structures 1520mm apart.   The concrete slabs for these structures are between 120mm and 150mm higher than the (uneven) concrete verandah between them.  

Looking to use 90 x 45 joists with merbau decking. 

Looking for advice on joist fixing. Best to hang the joists at 450mm spacing from the slabs or L bracket to verandah? As the deck will connect two doorways it would be a very simple task to level by hanging from the slabs but is that sturdy enough or anything else I should consider?  

[MitchellMc]

Welcome to the Bunnings Workshop community @Prybar. It's wonderful to have you join us, and many thanks for your question about constructing a deck.

You might like to post some images of the space so our members can better understand what you're working with. They'll then be able to provide informed responses. Let me know if you need a hand uploading photos.

It sounds like it might be best to create a frame to suit the area and then run your joists within the frame. The frame and joists can be supported from the ground on pedestal feet. The frame that runs around the perimeter against the sides of the slabs can be Dynabolted into the slabs for additional support. 

The joists will be spaced at 450mm, but the span of 1520mm is too far for 90 x 45mm, so you'll need to support each joist midway so they only span 750mm.

Please let me know if you have any questions.

Mitchell
 

[Prybar]

Thanks, to negate the need to break up the span can 90 x 45 mgp10 be used. I see they come in 3m lengths so would that be OK, with 10mm short on each end.  Cheers. 

[MitchellMc]

The maximum span of 90 x 45mm mgp10 used for joists on a deck is around 1000mm @Prybar. Any further than that, and you risk ending up with a bouncy deck. 1520mm is far outside its span abilities, so if that's how far they need to stretch, then there's no other option than to support them midway. 

I'm not sure if I follow this: "I see they come in 3m lengths so would that be OK, with 10mm short on each end." An image of the area indicating your intentions would be really helpful.

Mitchell

[Prybar]

Thanks, and apologies for lack of clarity.  I was looking at halving the 3m lengths and getting 2 x 1500mm lengths but it appears that it is not suitable anyway. Thanks for your advice. Cheers. 

[MitchellMc]

Oh, right! Thanks for clarifying @Prybar. If you follow my advice about creating a frame, then that would take care of the difference and allow you to use the 3000mm lengths. 1520 - 90mm (45mm frame on either side) = 1430mm. So, one 3000mm will give you two joists each.

Mitchell